Enzymes : Classification Active Sites , Models and Inhibition MCQ - Practice Questions with Answers

Enzymes and Their Classification

• An enzyme is a protein molecule that acts as a biological catalyst to speed up the metabolic reaction occurring inside the cells. 
• Enzymes are not consumed during the metabolic reactions.
• However, not all enzymes are made up of proteins. Ribozymes are catalytic RNA molecules that have enzymatic action during synthesis of proteins.
• Enzymes greatly increase the rate at which reaction takes place.
• They help in transforming one energy form into a more usable form.
• Many enzymes have been named by adding the suffix "-ase" to the name of their substrate or to a word or phrase describing their activity. 
• For example, DNA polymerase catalyzes the synthesis of DNA.

Chemical Nature Of Enzymes:
1. Simple Enzymes: 

• These are completely made up of proteins.
• Active site is formed by specific grouping of its own amino acids. 
• Additional substance or group is absent, e.g., pepsin, trypsin, urease.

2. Conjugate Enzyme:

• It is an enzyme that has two parts- a protein part called apoenzyme (e.g., flavoprotein) and a non protein part named cofactor. 
• The complete conjugate enzyme, consisting of an apoenzyme and a cofactor, is called holoenzyme. 
• Active site is formed jointly the apoenzyme and cofactor.

Enzymes are classified according to the reaction they catalyse. There are following types of enzymes:

1. Oxidoreductases or Dehydrogenases: catalyze the transfer of hydrogen and electrons from one redox system to another.
2. Transferases: catalyze the transfer of groups from one molecule to another.
3. Hydrolases: these cause cleavage of bonds using water.
4. Lyases: also known as synthases; catalyze reactions involving either the cleavage or formation of chemical bonds; cleavage of bond does not require water.
5. Isomerases: move groups within a molecule, without changing the gross composition of the substrate.
6. Ligases: these are energy-dependent and are therefore always coupled to the hydrolysis of nucleoside triphosphates